Oxymethylene polymers having olefinic double bonds in the polymer chain



United States Patent 3,385,832 OXYMETHYLENE POIPYMERS HAVING ULEFENKCDOUBLE BONDS IN THE POLYMER CHAEN Brian Edmund Jennings, Weiwyn, and.l'ohn Brewster Rose, St. Albans, England, assignors to ImperialChernical Industries Limited, London, England, a corporation of GreatBritain No Drawing. Continuation-impart of application Ser. No. 244,021,Dec. 12, 1962. This application Sept. 28, 1964, Ser. No. 399,910

3 Claims. (61. EGO-73) The present invention relates to a process forthe preparation of oxymethylene polymers and to the oxyrnethylenepolymers so prepared. It is a continuation-in-part of our application,Ser. No. 244,( 2l, filed Dec. 12, 1962, now abandoned.

Oxymethylene polymers, sometimes known as polyoxymethylenes, arepolymers having repeating units of the structure -OCH and may bederived, for example, for example, from the polymerisation offormaldehyde, e.g. as described in British patent specification 748,836,or from the polymerisation of its cyclic trimer trioxane, for instanceas described in British patent specification 877,820.

Homopolyoxymethylenes are thermally unstable and degrade by at least twomechanisms. The first involves depolymerisation from the thermallyunstable terminal oxymethylene hydroxide (-OCI-I OH) groups and occurseven at moderate temperatures. The second, requiring more severeconditions, involves chain scission followed by deploymerisation fromthe ruptured ends. Under severe conditions, the homopolymers may bedepolymerised completely.

In order to avoid or reduce the chances of degradation at moderatetemperatures by depolymerisation from the terminal oxymethylenehydroxide groups, it has been ro posed to react the homopolymers withcompounds that will substitute for the hydroxyl groups end groups whichare more stable to elevated temperatures, for instance the polymer maybe reacted with acid anhydrides, u-chloroalkyl ethers, alkyl halides,isocyanates and epoxides. However, the products are still subject todegradation by chain scission and once the polymer chain has beenruptured, the two broken halves may still depolymerize completely underforcing conditions. In order to reduce the effects of such degradationit has been proposed to copolymerise trioxane with other saturatedaliphatic cyclic ethers, principally dioxolane. The copolymerisation hasthe effect of introducing into the polymer chain groups having adjacentcarbon atoms in the chain itself. Thus, the copolymers contain bothoxymethylene (OCH groups and divalent organic groups (-OR) havingadjacent carbon atoms and derived from the comonomer. For instance, inthe case where dioxolane is the comonomer, the divalent organic groupshave the structure OCH CH When the copolymer is subjected to conditionscausing chain scission, depolymerisation from the ruptured ends proceedsonly as far as the first OR- group in the chain and there halts, thuspreventing total depolymerisation.

Homopolyoxymethylenes are also crystalline and like the polyamides theysuffer from sharply defined melt ing points; that is, the differencebetween the temperature at which the polymer starts to melt and that atwhich it is wholly molten is small. Because of this, the conditionsrequired for processing the polymers (e.g. by moulding or extrusion) arecritical and in particular this causes difficulty in the manufacture andorientation of films. Copolymerisation has the additional advantage ofwidening the melting range, thus reducing the criticality of theoperating conditions required for successful fabrication.

However, introduction into the oxyrnethylene polymer chain of theresidues of other saturated cyclic ethers also has the undesirabletendency of affecting adversely the unique and commercially attractivecombination of physical properties (toughness, rigidity and high meltingpoint) that is associated with homopolyoxymethylenes.

It is an object of the present invention to provide oxymethylenepolymers which in high molecular weight form have good thermalstability, a useful melting range and yet retain a high ultimate meltingpoint. It is a further object of the invention to provide oxymethylenepolymers which may be chemically modified and may be crosslinked.

According to the present invention we provide a copolymer comprising theproduct of polymerising a cyclic oligomer of formaldehyde, preferablytrioxane, with a cyclic ether having the structure:

where R is a divalent radical having a monoethylenically unsaturatedchain of from 4 to 5 carbon atoms linking the oxygen atoms of the ether,each of the remaining valencies of said carbon atoms being satisfied bya monovalent radical selected from the group consisting of hydrogenatoms, halogen atoms (for instance, chlorine, bromine, fluorine andiodine) and alkyl groups having up to 2 carbon atoms and R and R areeach selected from the group consisting of hydrogen atoms and monovalenthydrocarbon radicals having from 1 to 6 carbon atoms.

Of the cyclic oligomers of formaldehyde, we prefer trioxane because ofits ready availability. Tetraoxymethylene is an example of another suchcyclic oligomer.

The cyclic ethers may be derived by the reaction of a suitable aliphaticethylenically unsaturated diol with an aldehyde or ketone. Examples ofaldehydes and ketones that may be used are formaldehyde, acetaldehyde,propionaldehyde, n-butyraldehyde, iso-butyraldehyde, nvaleraldehyde,benzaldehyde, acetone, methyl ethyl ketone, di-ethyl ketone,acetophenone and benzophenone. The ethers derived from formaldehyde areformals, those derived from other aldehydes are acetals and thosederived from ketones are ketals.

Aliphatic ethylenically unsaturated diols that may be used to form ourethers are those having a monoethylenically unsaturated chain of 4 to 5carbon atoms linking the two hydroxyl groups. They include, for example,butene-1,4-diols, pentene-l,5-diols and their derivatives in which oneor more of the hydrogen atoms bound to the carbon atoms have beenreplaced by halogen atoms, methyl groups and ethyl groups. Examples arebut-Z-ene- 1,4-diol, pent-2-ene-L4-diol, hex-3-ene-2,5-diol, oct-4-ene-3,6-diol, 1,4-dichlorobut-2-ene-1,4-diol,2,5-dimethylhex-3-ene-2,5-diol and 3,6-dimethyloct-4-ene-3,6-diol. Ofthese, we prefer those diols having ethylenic unsaturation in the chainbetween two methylene hydroxide groups because the cyclic etherderivatives of these compounds may be copolymerised with trioxane withease. But-2-ene-1,4-diol is our preferred diol because of its ease ofmanufacture from readily available materials.

Our preferred ethers are the formals and acetals f but-2-ene-l,4-diol,particularly 1,3-dioxep-5-ene and 2- isopropyl-l,3-dioxep-5-ene, becauseof their case of copolymerisation with trioxane. The formal may becopolymerised to give very useful products of high molecular weight,suitable for extrusion and moulding.

Our copolymers are formed of units having the structure -OCH and unitshaving the structure where R, R and R are as hereinbefore defined.

In order to obtain products of good physical properties, it is preferredthat at least 50% of the units forming the polymer chain of thecopolymer are oxymethylene (OCH units. Those in which at least 80% ofthe units are oxymethylene units are generally suitable as thermoplasticmaterials. Copolymer in which at least 90% of the units are oxymethyleneunits are generally tough, rigid and very suitable for moulding. Toobtain products showing a useful improvement in thermal stability overthe homopolymers, we prefer that at least 0.1% and generally at least0.4% of the units forming the polymer chain are other than oxymethyleneunits. Copolymers in which from 95 to 98.5% of the units areoxymethylene units have a very useful combination of thermal stability,melting range, toughness and rigidity and are very useful moulding andextrusion materials.

Copolymers with polymer chains containing less than 80% of oxymethyleneunits tend to have substantially reduced rigidity and softening pointand, as the amount of these units in the copolymers increases further,tend to become waxy; they are more suitable a plasticisers, lubricantsand additives for lubricants, polishes, viscosity depressants and thelike.

When considering the composition of our polymers, it must be rememberedthat where the comonomer is a cyclic formal the units forming thepolymer chain are -OCH units and OROCH units. In such cases the --OCHunits of the OROCH units must be added to the OCH units derived from thetrioxane in order to calculate the total percent of OCH units in thepolymer chain.

Particularly useful polymers are obtained when their molecular weight isat least 15,000 and preferably 20,000 or more. A molecular weight of20,000 is approximately equivalent to an Inherent Viscosity of 1.0 asmeasured as a 0.5% solution in p-chlorophenol containing 2% of a-pineneat 60 C.

Further according to the present invention we provide a process for thepreparation of high molecular weight oxymethylene polymers whichcomprises subjecting to a temperature of at least C. a mixturecomprising (i) trioxane, (ii) from 0.003 to 3 moles per mole of trioxaneof a cyclic ether having the structure:

as hereinbefore defined and (iii) from 0.0001 to 0.1 part of anelectrophilic catalyst per 100 parts of the combination of trioxane andcyclic ether and recovering a copolymer of trioxane and said cyclicether.

The process of the invention not only provides a method of obtainingcopolyrners having a most useful combination of wide melting range, highultimate melting point, rigidity and toughness but is a useful methodfor inserting into the polymer chain ethylenically unsaturated units thepresence of which allows the polymer to be chemically modified orcross-linked and also encourages the adhesion of paint to an articlefabricated from the polymer. The latter property is particularlyadvantageous where the polymer is to be used in metal replacementfields.

The polymerisation may be effected in bulk or in solution.

Where a bulk process is used, the polymerisation is normally carried outat a temperature at which the polymerisable material is in a molten orsubstantially molten form. However, for the preparation of highmolecular weight polymers, e.g. polymers of molecular weight greaterthan 15,000 the polymerisation temperature should not be so high as toallow substantial depolymerisation to occur. It is preferred, on theother hand, that a temperature is used at which the cyclic ether issoluble in trioxane.

It is preferred to effect the polymerisation at temperatures of fromabout 0 to about C. and preferably 5090 C. but hi her temperatures maybe used if desired. Where the polymerisation is effected underconditions of shear, for example in a mixer, it is often desirable touse polymerisation temperatures as high as C. Where it is desired to usetemperatures of above about C. (the boiling point of trioxane) thepolymerisation should be carried out under super-atmospheric pressure.

Where the polymerisation is effected in solution, the cyclic ether ispreferably one which is soluble in the mixture of trioxane and solvent.Suitable solvents include hydrocarbons such as hexane, heptane,cyclohexane, benzene, toluene and xylene and chlorinated hydrocarbonssuch as methylene chloride, chloroform or carbon tetrachloride. It ispreferred to effect the polymerisation at a temperature high enough toprevent the polymerisable compound from crystallising out of solutionbut at a temperature not above the boiling point of the solution at theworking pressure. The polymerisation may be effected undersupenatmospheric pressure if desired and this is useful since it permitshigher temperatures to be used.

The polymerisation may take place satisfactorily in the presence of verysmall amounts of water such as would be found as impurities incommercial grades of the oligomer or the cyclic ether but, as is knownto polymerisation experts, if good yields of high molecular weightmaterial are to be obtained it is preferred to remove substantially alltraces of water from the polymerisation medium. We prefer that thepolymerisation medium contains less than 0.05% by weight of water, morepreferably less than 0.03%.

Any electrophilic catalyst known for the polymerisation of trioxane maybe used in the polymerisation. Such catalysts may be known,alternatively, as cationic catalysts or initiators. Examples are foundin U.S. specification 2,795,571, US. specification 2,947,727, U.S.specification 2,947,728, US. specification 2,989,511, French patentspecification 1,221,148, Belgian patent specification 585,- 335, Belgianpatent specification 585,980 (in particular) and British patentspecification Nos. 875,558; 877,820 and 878,163. More particularly,these include Lewis acids, Friedel-Craft catalysts, elementary iodine,perchloric acid and acetyl perchlorate. Of these, Lewis acids which arehalides are preferred and boron trifluoride in particular has been foundto give very good results. The boron trifiuoride may be used inunmodified form or as one of its coordination complexes with an oxygen,sulphur, nitrogen or phosphorus compound (for instance as described inUS. specification No. 2,989,511, British patent specification No.877,820 and Belgian patent specification No. 585,980.) Examples of suchcomplexes include those with water, with organic compounds having anoxygen or sulphur atom which may act as the donor atom (e.g. alcohols,phenols, ethers, acids, anhydrides, esters, ketones, aldehydes,thioethers and mercaptans), with organic compounds having a trivalentnitrogen or phosphorus atom (e.g. aryl amines, heterocyclic nitrogencompounds, amino acids, hydrazides, amides, phosphine and organicphosphines) and fluoborate complexes such as those with diazoniurn andoxonium compounds. Where the catalyst is a co-ordination complex, it isto be understood that it should be used in amounts equivalent to thoserequired to yield from 0.0001 to 0.1 part of the Lewis acid per 100parts by weight of monomeric material.

The molecular weight of the products of the invention may be controlledby adding chain transfer agents to the polymerisation medium, suitablechain transfer agents being chlorinated hydrocarbons, alkyl acetates andacetals. It is preferred to effect the polymerisation in the sub-'stantial absence of oxygen.

Particularly useful products, in which from about 90 to about 99.6% ofthe units in the chain are oxymethylene units, are obtained bypolymerising from about twelve one thousandths to about three eighths ofa mole of cyclic ether per mole of trioxane. Products having the optimumcombination of melting range, rigidity, toughness and processibility aregenerally formed by polymerising from about five one hundredths to aboutone sixth of a mole of cyclic ether per mole of trioxane.

We prefer that the polymerisation is effected in bulk or in the presenceof only very small amounts of solvent since then the necessity ofexpensive solvent extraction and recovery processes may be avoided.

In a process according to our invention, the cyclic ether and trioxaneare first carefully dried and are then added to a pre-dried reactor suchas a steel bomb. The container may be swept with nitrogen gas and thecatalyst is then added alone or as a solution in an inert organicsolvent. The container is sealed and heated to about 65 C. and thepolymerisation is allowed to take place. After the required time, thepolymerisation is brought to a conclusion and the reactor will containthe poly-.eric products and catalyst residues and possibly unreactedtrioxane and unreacted cyclic ether.

In the production of high polymers as described above the polymerisationtemperature is normally less than the softening point of the polymers.As the polymers formed are usually insoluble in the mixture of monomers,the product of a bulk polymerisation process is usually a crumbly mass.To ensure good mixing of the polymerisation and so full growth of thepolymer chains, and to form an easily worked powder at the end of thepolymerisation, it is desirable to apply shear to the polymerisationmixture during the bulk process.

Conditions of shear may be imposed by any suitable means, such asintense stirring or agitation and the polymerisation may, for example,be carried in a simple mixer. A vessel rotatable on a horizontal axisand having within it freely rolling spheres, rods or the like asdescribed in the specification of British Patent No. 749,086 may also beused.

Very good results may be obtained if the polymerisation ingredients arefed into a continuous mixer having a screw with an interrupted threadplaced in a cylindrical body, the inside surface of which has rows ofprotruding teeth. The screw is made both to rotate and reciprocate sothat the teeth on the wall of the cylindrical body pass through thebreaks in the screw thread. In this case the polymerisation mass movesforward along a path which has a generally helicoidal shape with analternate forward and backward movement as it moves towards the outlet.The use of this mixer also has the advantage in that a continuousprocess may be used. A suitable machine is described in thespecification of British Patent No. 626,- 067. A sigma-bladed mixer isalso suitable.

Therefore, in another process according to the invention the cyclicether and trioxane are first carefully dried and then added togetherwith the catalyst to the pro-dried mixer which is heated to the desiredtemperature. The polymerisation takes place in the mixer which may bepressurised if desired and the polymer is removed from the other end ofthe mixer in the form of a slurry or powder.

The material so obtained will contain the polymeric product, catalystresidues and possibly unreacted trioxane and unreacted cyclic ether; thepolymeric product comprises the copolymer of trioxane and the cyclicether and possibly incidental polyoxymethylenes derived from thehomopolymerisation of the trioxane. The catalyst residues are preferablyremoved as soon after the polymerisation as possible since theirpresence may also catalyse the decomposition of the polymeric product;they may be removed simply by washing the mix with an aqueous,

preferably an aqueous alkaline wash. For example, the mix may be washedwith a dilute ammoniacal or caustic soda solution. As is well known,solvents may also be used for removing these catalysts. During theirremoval the polymer may also be stabilised as is set out below.

The unreacted trioxane and any of the cyclic ether may be separated fromthe copolymer by any suitable means such as filtration or solventextraction. Since trioxane is soluble in most common solvents, it may beseparated by a solvent extraction process, e.g. at the same time as thecatalyst is removed. The cyclic ether may also be extracted by a solventextraction process.

The presence of the incidental polyoxymethylene may adversely affect thestability of the material and this may be remedied either bypreferential destruction or by endgroup stabilisation of thispolyoxymethylene.

The coplymers prepared by the process of the invention contain bothoxymethylene groups derived from the trioxane and divalent organicradicals derived from the cyclic ether and the copolymer chains maytherefore be ended by terminal groups of the structure OCH OH or theymay be ended by other groups derived from the cyclic ether. Where acopolymer chain is terminated by a --OCH OH group, which is readilydetachable on heating or under alkaline conditions, the end of the chainmay be represented as having the structure where n is a whole number andR is the alkylidene radical derived from the cyclic ether and nearest tothe end of the polymer chain. On subjecting the copolymer chain to athermal or alkaline degradation reaction, the -O-CH 0H group will bedetached and the oxymethylene group immediately behind it (if any) willreceive a hydrogen atom and become an OCH OH group and the chain willnow have the structure This next O-'CH OH group now is attacked 'and thedegradation of the chain will continue until the group is reached. Sincethe ROH group is relatively much more resistant to detachment, thedegradation reaction will normally halt there. The copolymer maytherefore be stabilised either by subjecting it to such a degradationreaction or by end-group stabilising it. It will be appreciated thatunder such degradation conditions, any homopolyoxymethylene that may bepresent will eventually be degraded completely if conditions aresufhciently forcing.

Where it is preferred to destroy the incidental polyoxymethylene and toremove the unstable oxymethylene endgroups from the copolymer, this maybe done simply by heating the mixture in an inert atmosphere, e.g. undernitrogen at a temperature of about C. or above after the catalystresidues have been removed; it is preferred not to use too high atemperature since otherwise the copolymer may also be degraded to anundesirable extent. The preferential destruction may 'also be aided bythe addition of a weak acid such as formic acid or acetic acid or analkali such as caustic soda but the latter is not to be preferred as itmay tend to cause undesirable degradation of the coploymer and mayconvert the formaldehyde so generated into sugar-like polymers.

Stabilisation by removal of these unstable entities may be carried outin an alkaline process for removing the polymerisation catalyst and inthis preferred process, the polymer is treated with a basic, preferablyammoniacal, solution at moderately elevated temperatures. However, it isbelieved that the action of the basic solution may be merelytopochemical (see, for instance, pages 231 'and 232 of DieHochmolekularen Organischen Verbindungen by Staudinger, 1932) and for anefficient reaction the polymer is preferably treated either in a finelydivided state or, more preferably, in solution and the formation of asolution may be encouraged by carrying out the process under elevatedpressure and temperature. The advantage of such a process is that in onestep the catalyst, unreacted trioxane and incidentalhomopolyoxymethylene may 'all be removed from the polymer. When thesolution is cooled, the desired stable oxymethylene copolymer comes outof solution and may be separated.

Instead of a strong, ammoniacal solution, a solution of an amine, or anamide or an 'alkali hydroxide such as sodium or potassium hydroxide or asalt of a strong base and weak acid such as sodium carbonate or sodiumacet'ate may be used alone or in combination under similar This isexemplified by a series of experiments performed to compare theproperties of copolymers formed from the typical prior art comonomer,dioxolane, and the cyclic formal of but 2-ene-l,4-diol (1,3-dioxep-5-ene), representing our specified class of comonomer. The amount of eachmonomer (calculated as mole percent based on the molar amount of OCHunits present in the form of trioxane in the polymerisation mixture) andthe melting range of the appropriate copolymer after it had beenseparated from the reaction mixture and catalyst residues, treated tothe ammoniacal wash described hereinbefore and pressed into a film iscompared for each polymerisation in the table below.

Amountof comonomer in polymerisation mixture (mole conditions. Thesolvent may be water or preferably a mixture of water with awater-miscible alcohol (particularly methanol), with a water-miscibleketone such as acetone or with an ether. The presence of the organicmaterial helps to bring the polymeric material into solution.

When on the other hand it is preferred to end-group stabilise theincidental homopolyoxymethylene and the oxymethylene end-groups of thecopolymer, the mixture may be reacted with any suitable compound whichwill substitute for the terminal hydroxy group of the polyoxymethyleneor copolymer other groups (such as acetate, ether or urethane groups)which are relatively more stable. The end-group stabilisation may beeffected for example, by reacting the copolymer mixture with acarboxylic acid, a carboxylic acid ester, a carboxylic acid anhydride,an alcohol, an acetal, an isocyanate, an ortho ester, 2. ketal, an orthocarbonate, a ketone, a ketone/ketone transformation product, an ether ortheir substituted derivatives, an epoxide such as ethylene oxide orpropylene oxide, an olefine such as butadiene or styrene, an alkylhalide such as tertiary butyl chloride or a vinyl monomer such asacrylonitrile or acrolein. Reaction with a carboxylic acid anhydridesuch as acetic anhydride is preferred.

The copolymer may be further stabilised against degradation by theaddition of any suitable stabiliser for the polyoxymethylene. Suitablestabilisers include, for example, hydrazines, amines, amidines, amides,polyamides, phenols, substituted phenols, polynuclear phenols(particularly alkylene bis-phenols), ureas, thioureas, quinones such asthose described in our copending application Ser. No. 236,716 nowabandoned and certain aromatic nitro compound, such as those describedin our copending application Ser. No. 252,555, now U.S. Patent No.3,261,- 805 alone or in combination. Stabilisers against attack by ultraviolet light, such as hydroxy-substituted benzophenones, may also beincorporated into the polymer. Fillers, pigments, mould release agents,lubricants, plasticisers, and the like may also be added and the polymermay be blended with other compatible polymeric materials.

The copolymers of the present invention differ from the products ofcopolymerising trioxane with the cyclic ethers known hitherto. Forequivalent comonomer contents, the ultimate melting points of ourspecified copolymers are generally higher than those of the knowncopolymers while the melting range is greater. Alternatively, to matchthe melting range of a known copolymer, less comonomer is required inour specified copolymers, thus reducing the undesirable modifications tophysical properties caused by introducing comonomer residues into theoxymethylene chain.

The T and T of the copolymer are measured by placing a thin film ofcopolymer 10-60 1. in thickness (which has been fused at 20-30 C. abovethe melting point and then cooled at a rate of 6 C. per hour) on a glassslide and under a glass cover, raising its temperature by 1 C. perminute on a hot stage between the crossed polars of a microscope andmeasuring the birefringence of the sample as the temperature isincreased. The birefringence may be measured by observation of theintensity of light allowed to pass the analyser of the microscope andthis intensity may be recorded suitably by a photoconductor. T (theultimate melting point) is the temperature at which the light intensityhas fallen from its initial value at room temperature to a constantminimum level and T is the temperature at which the light intensity hasfallen to exactly mid-way between these two levels. The range T -T isdirectly indicative of the melting range of the copolymer.

From the table it may be seen that the molar amount of comonomerrequired to give a desired melting range (say 7 C.) is very much less inthe case of l,3-dioxep- S-ene than in the case of dioxolane and that forsuch a melting range, the copolymer from 1,3-dioxep-5-ene has a meltingpoint several degrees higher than the copolymer from dioxolane.

The drop in melting point that occurs with the introduction of ourcopolymer and the wide melting range both indicate that our specifiedcopolymers are of the random variety and are not block copolymers. Blockcopolymers having such small amounts of the cyclic ether would beexpected to have melting points even closer to that of the homopolymerderived from trioxane and to have a narrower melting range.

Because of the width of melting range of our copolymers, the conditionsrequired for moulding or otherwise fabricating them in massive form arenot as critical as those required for the homopolymer and they lendthemselves, therefore, to easier fabrication. Of particular interest isthe orientation of films Where it is desirable to be able to operatewithin as wide a range of tempera tures as possible, the lower limit isgoverned by the minimum temperature of uniform drawing and the upper bythe temperature at which flow instead of orientation occurs.

The rate of thermal degradation of the copolymers, particularly of thosewhich have been stabilised by the methods described, is also less thanthat of copolymers of trioxane having equivalent amounts of dioxolane.For example, we found that the rate of loss in weight at 222 C. of acopolymer formed by polymerising trioxam: with 2.5 mole percent(calculated on the amount of CH O present as trioxane) of dioxane, afterthe ammoniacal wash treatment described hereinbefore, is 0.15 per minutewhile the equivalent rate for the copolymer obtained by polymerisingtrioxane with 2.5 mole percent (calculated on CH O present as trioxane)of 1,3-dioxep- S-ene, after the same ammoniacal wash treatment, is only0.02% per minute. That for the homopolymer of trioxane, without theammoniacal wash treatment which would decompose it, is about 3% perminute. (The test for estimating loss in weight was effected by placinga weighed amount of the copolymer in an ampoule having a narrow neckbent through about 180 and open to the atmosphere and immersing theampoule so that about its lower two thirds were immersed in the vapoursof boiling methyl salicylate. The ampoule is removed at regular timedintervals, cooled in ice and reweighed and the cycle is repeated. Thetests are carried out over a period of at least 20 minutes, generally atleast 100 minutes. Some of these tests were carried out under anatmosphere of nitrogen.) The surprising stability of our copolymers attemperatures well in excess of their melting points makes them eminentlysuitable in the manufacture of articles which may be subjected duringtheir life to elevated temperature (for example as insulants in electrical switch gear).

Our copolymers in which at least 90% of the units in the chain areoxymethylene groups are tough and dimensionally stable at or above roomtemperature and their very low rate of thermal degradation coupled withtheir unexpectedly wide melting ranges makes them particularly useful asmolding materials (eg. for use in injection moulding, compressionmoulding and extrusion processes) and for the melt-spinning and castingof fibres and films. We prefer our mould'able polymer to have a T ofabout 150 C. or more. They may also be solvent cast to given films orsolvent spun to give fibres from suitable solvents, examples of whichare oand p-chlorophenol, benzyl alcohol and et-naphthol. These polymersmay be used, for example, in the light engineering industry for themanufacture of small gear, rollers bear: ings, bushes, clips and cams;in the motor industry for the manufacture of dust covers or caps forgrease nipples and bearings such as track-rod joints, lamp covers,instrument housings, low stressed gears such as oil pump gears,speedometer gears and windscreen wiper gears, self-lock nuts and othersmall mouldings. Our copolymcrs containing lesser amounts ofoxymethylene groups have reduced strength, rigidity and softening point,but are suitable as plasticisers, lubricants, etc. Because of thepresence of unsaturated linkages in the polymeric chain, our polymersare particularly suitable in applications where chemical modification ofthe products is desirable and in applications (for example Where theyare to replace metals) where the shaped products are to be painted.

The invention is illustrated by the following examples in which allparts are expressed as parts by weight.

Example I A mixture of 30.6 parts of trioxane (which had been distilledfrom sodium and had a water content of less than 0.002%) and 3.36 partsof the cyclic monoformal of but-2-ene-l,4-diol(1,3-dioxyacylohept-5-eue) which had also been distilled from sodium wasmelted at 81 C. in a clean dry glass apparatus under an atmosphere ofdry nitrogen. When a homogeneous melt was obtained 0.034 part borontrifluoride diethyl etherate dissolved in 2 parts of dry diethyl etherwas injected into the melt. After 18 minutes polymerisation commencedand was complete in 3 minutes. The hard white polymer was removed fromthe vessel, ground to a coarse granular powder and refluxed with amixture of 100 parts of 880 ammonia, 100 parts of methanol, and 800parts of water for two hours. After filtering, washing with water, anddrying at 60 C. in vacuum for 16 hours, 26.7 parts of polymer wereobtained. The rate of loss in weight of this polymer at 222 C. in anitrogen atmosphere was 1.4%

per minute for the first 9% loss and thereafter 0.05% per minute. Therate of loss in weight for a homopolyoxymethylene formed from trioxanewas 3.0% per minute under the same conditions.

A film which was melt pressed at 180-185 C. from the polymer was toughand highly crystalline and had a melting range as determined on a hotstage microscope of 160 C. (50% molten) to 166 C. (100% molten) whereasa homopolymer, prepared from trioxane alone under similar conditions,had a crystal melting point of 170 C.

Example H 28.7 parts of trioxane and 3.15 parts of the cyclic formal ofbut-2-ene-1,4-diol were polymerised as in Example I in the presence of0.032 part boron trifluoride etherate in 0.64 part diethyl ether. Thepolymerisation was effected at 805 C. and the yield after ammoniatreatment was 27.4 parts of a polymer having a breakdown rate, asmeasured at 222 C. in an atmosphere of nitrogen, of 0.04% per minute.

, A tough film was melt pressed from the polymer at 190 C. and thepolymer had a melting range of 158- 165 C. Infra-red analysis indicatedthat the polymer contained 1.1 mole percent of but-Z-ene diol residues.

Example III The process of Example I was repeated at a temperature of C.using 35.6 parts trioxane, 5.93 parts of the cyclic formal ofbut-2-ene-1,4-diol and 0.0395 part boron trifluoride etherate in 0.79part diethyl ether.

A polymer was obtained having a breakdown rate after ammonia treatment,as measured at 222 C. in an atmosphere of nitrogen, of 0.37% per minuteto 3% loss and thereafter 0.06% per minute. The melting range of thepolymer was 147l54 C. Infrared analysis indicated that the polymercontained 3.5 mole percent of but-Z-ene diol residues.

Example IV The process of Example I was repeated at a temperature of 80C. using 33.5 parts trioxane, 8.93 parts of the cyclic formal ofbut-2-ene-l,4-diol and 0.42 part boron trifiuoride etherate in 0.85 partdiethyl ether. There was an induction period of 10 minutes beforepolymerisation commenced followed by rapid polymerisation.

A polymer was obtained having a breakdown rate, as measured at 222 C. inan atmosphere of nitrogen, of 0.065% per minute for the first 2% lossand thereafter 0.004% per minute. The melting range of the polymer wasl32146 C.

Example V A solution of 34.2 parts trioxane and 3.76 parts of the cyclicformal of but-2-ene-1,4-diol in parts of pure methylene chloride wasprepared and the solution was refluxed in an atmosphere of dry nitrogen.0.008 part of boron trifluoride diethyl etherate was added as a solutionin diethyl ether. The mixture turned pale green and polymer began toprecipitate out of the solution. After a further two hours refluxing thefine powder was filtered off and treated as in Example I.

24 parts of a white powder which had a breakdown rate of 0.15% perminute at 222 C. were obtained.

Example VI A jacketed stainless steel sigma-bladed Baker-Perkins mixerfitted with a close-fitting lid having a nitrogen inlet and outlet, arubber injection cap, a glass window, and a trap for charging the vesselwithout allowing air to come into contact with the reactants was usedfor the polymerisation. Prior to conducting the experiment the vesselwas thoroughly dried by passing a rapid stream of nitrogen at about C.through it for 16 hours. The vessel was then charged with 497 parts oftrioxane which had been dried by passage down an activated aluminacolumn at 70 C. and subsequent distillation from calcium hydridefollowed by 24.9 parts of the cyclic formal of 1,4-but-2-ene diol(1,3-dioxep-5-ene) and 66 parts of cyclohexane both of which had beendried by distillation from calcium hydride. The mixture was stirred at60 C. and 0.0693 part of boron trifluoride di-n-butyl etherate in 0.857part dry cyclohexane was injected into the solution. After 9 minutes thepolymer began to form, within an other 4 minutes a dough-like mixturewas obtained and after 25 minutes the mixture was quite dry and finelypowdered. The polymerisation was stopped after 2% hours by adding asolution of 1 part of tri-n-butylamine in 300 parts of methyl ethylketone. Stirring was continued for another hour after which the vesselwas emptied and the cream coloured polymer was filtered off, washedtwice with 300 parts of acetone and finally dried for 16 hours at 50 C.under vacuum. The yield of white powder was 312 parts and it had aninherent viscosity of 1.36 as determined on a 0.1% solution inp-chlorophenol containimz 2% of a-pinene.

In order to remove homopolymer and unstable oxymethylene hydroxyl endgroups from the copolymer and any catalyst residues, 200 parts of thepolymer were dissolved in 2,400 parts of methanol, 1,600 parts of waterand 40 parts of 880 ammonia at 150 C. in a stirred autoclave. Aftertreatment the mixture was rapidly cooled. The resulting precipitate waswashed with water and dried at 60 C. under vacuum for 16 hours andreadily divided into 120 parts of fibrous material and 60 parts ofpowder. The fibrous material had an inherent viscosity of 1.4 and thepowder an inherent viscosity of 0.3 and analysis showed that the formercontained 1.3 mole percent, and the latter 1.8 mole percent of buteneformal residues. The fibrous polymer had a breakdown rate at 222 C. of0.1% per minute and a melt flow index (at 190 C. and a load of 2kilograms) of 6.9. It was compounded at 170 C. on open rolls withantioxidants and compression moulded at 180 C. to give tough, flexiblewhite fibres 0.015 inch thick having the following tensile properties:

Strong fibres could be melt-spun from the sample at 190 C.

A sample of the fibrous polymer was completely hydrolysed withconcentrated hydrochloric acid and the resultant but-2-ene-1,4-diol wastitrated for ethylenic unsaturation against a 0.002 molar solution ofbromide and bromate to an amperometric end point. It was found that thediol lost its unsaturation at the rate of 0.4% per hour upon standing ina mixture of formaldehyde and concentrated hydrochloric acid andtherefore the bromide/bromate solution was standardised against a but-2-ene-1,4-diol sample that had stood in the same environment for the sametime as the test sample.

By this method, the copolymer was found to contain 3.6% by weight ofbut-2-ene-1,4-diol residues, equivalent to 1.63% molar.

Example VII 48.6 parts of trioxane were dried by refluxing with sodiummetal for 24 hours and then adding a little benzophenone and continuingheating for 4 hours until a deep blue colour persisted. Distillationfrom this mixture gave trioxane containing 0.02% by weight of water asmeasured by the intensity of the O-H stretching absorption band at 2.71microns wavelength in the Infra-red. A solution of this trioxane in 49parts of dry cyclohexane and 3.24 parts of dry butene formal was stirredat 61 C. and 0.0109 part ferric chloride in 0.71 part dry ether wasinjected into the mix. After 3 hours the resultant thick mixture wasfiltered and the residue was washed with acetone, dilute hydrochloricacid and water and dried at 60 C. under vacuum for 16 hours. 13 parts ofa cream powder were obtained. On heating with aqueous methanolic ammoniaat C. under pressure followed by washing and drying, 11 parts of verystable polymer were obtained.

Example VIII A solution of 47.2 parts of trioxane (which had been driedby distillation from calcium hydride) in 47 parts of dry methylenechloride and 3.15 parts of butene formal was stirred at 35 C. and asolution of 0.0324 part of boron trifluoride di-n-butyl etherate in 2.34parts of cyclohexane was added. After 24 hours 0.1 part oftri-n-butylamine was added. The white powder was filtered ofl, washedwith acetone and dried to yield 20.5 parts of the polymer. The residueafter treatment with aqueous methanolic ammonia at C. under pressure wasfound to have a breakdown rate at 222 C. of 0.08% per minute. Strongfibres could be spun from the molten polymer at C.

Example IX To a melted mixture of 35.8 parts of trioxane and 2.4 partsof butene formal at 70 C. was added a solution of 0.0129 part of FeCl in0.71 part of dry ether. After 15 minutes the reaction mixture was solidand it was ground up with acetone to extract unreacted trioxane, washedwith dilute hydrochloric acid and finally washed with water. The palecream powder was dried at 65 C. under vacuum to yield 15.9 parts ofpolymer. Upon heating under pressure at 150 C. with aqueous methanolicammonia, the product lost 13% of its weight leaving a polymer which hada breakdown rate at 222 C. of 0.04% per minute.

Example X A solution of 46.7 parts of dry trioxane and 3.11 parts ofbutene formal was prepared at 60 C. in 47 parts of dry benzene. To thisstirred solution was added a solution of 0.012 part of boron trifiuoridedi-n-butyl etherate in 0.73 part of ether. After 3 hours, 1l-25 parts ofcopolymer were obtained. After destroying catalyst residues and unstablepolymer by ammonia treatment, the polymer had a 222 breakdown rate of0.05% per minute.

Example XI A mixture of 2.94 parts of dry 2-isopropyl-1,3-dioxep- 5-eneand 41.1 parts of dry trioxane was prepared at 73 C. To the melt wasadded a solution of 0.01 part of boron trifiuoride diethyl etherate in0.73 part of dry diethyl ether. An immediate pink colour developed whichchanged to green when polymer was deposited after about 5 minutes andafter 20 minutes the mixture was solid. The polymer was ground up withacetone and then heated at 150 C. in a pressure vessel for /2 hour with400 parts of methanol, 400 parts of water and 5 parts of 880 ammonia.After washing well with hot water to remove the hexamethylene tetramineformed and drying the product for 16 hours at 60 C. in vacuum, 15.4parts of white polymer were obtained. This polymer had a first orderrate constant 'for loss in weight at 222 C. of 0.024% per minute up to90 minutes. Its melting range was from 144 to 152 C. Infra-red analysisshowed the presence of unsaturation in the polymer equivalent to about1.5 mole percent of 2-isopropyl 1,3-dioxep-5-ene.

Strong fibres could be spun from the molten polymer at 190 C.

Example X'H 59 parts of pure dry trioxane and 4.2 parts 2-isopropyl-1,3-dioxep-5-ene were dissolved in 59 parts of dry cyclohexane. Thesolution was stirred under nitrogen at 61 C. and a solution of 0.0363part of boron trifluon'de di-nbutyl etherate in 2.34 parts ofcyclohexane was added. The solution became green immediately and polymerbegan to form after 1 hour. The polymerization was allowed to continuefor 18 hours and was then terminated by the addition of 0.1 part oftri-n-butylamine. The cream powder was filtered ofi, washed well withacetone and dried at 60 C. in vacuum giving 10.7 parts of polymer. Onheating 13 10 parts of this product with aqueous methanolic ammonia at150 C., 7.4 parts of copolymer having a breakdown rate at 222 C. of0.11% per minute were obtained.

Example XIII A series of polymerisations between tn'oxane and1,3-dioxep-S-ene were carried out in the absence of solvent and usingboron trifluoride diethyl etherate as catalyst. The properties of thepolymers formed are set out below.

The process of Example I was repeated using 7.8 parts of4,4,7,7-tetrametl1yl-l,3-di0xep-5-ene as the comonomer in place of1,3-dioxep--ene. The crude polymeric product was worked up by theprocess described in Example I and pressed to give a film having amelting range of 142 C. (T to 161 C. (T

Example XV The process of Example I was repeated using 4.6 parts of4,7-dimethyl-4,7-diethyl-1,3-dioxep-5-ene as the comonomer in place of1,3-dioxep-5-ene. The crude polymeric product Was worked up as describedin Example I to give a film having a melting range of 136 C. (T to 150C. m)-

We claim:

1. A thermoplastic molding material suitable for film and fibermanufacture, which comprises a random copolymer of trioxane and a cyclicether having the structure in which X is selected from the groupconsisting of hydrogen and isopropyl, Y is selected from the groupconsisting of hydrogen and methyl and Z is selected from the groupconsisting of hydrogen, methyl and ethyl, which copolymer: (1) is madeusing an electrophilic catalyst, (2) has an ultimate melting point of atleast 146 C. and a melting range of at least 6 deg. C, (3) is free fromterminal O.CH .OH groups, and (4) consists of 95-985 mole percent of-O.CH units together with randomly distributed --O.CHX.O.CYZ.CH:CH.CYZ-units in the polymer chain.

2. A material according to claim 1 which comprises a random copolymer oftrioxane and 1,3-dioxep-5-ene.

3. A copolymer of trioxane and a cyclic formal of an unsaturateddihydric alcohol having 4 to 10 carbon atoms, said copolymer havingolefinic double bonds in the main chain and consisting of to 99.9 molepercent of O.CH units and 0.1 to 20 mole percent of units other thanO.CH derived from the cyclic formal.

References Cited UNITED STATES PATENTS 2,870,097 1/ 1959 Pattison 260-673,027,352 3/1962 Walling et a1. 260- 67 3,194,788 7/1965 Kullmar et al.260-67 3,210,297 10/ 1965 Fischer et a1 260-67 FOREIGN PATENTS 807,5891/ 1959 Great Britain.

WILLIAM H. SHORT, Primary Examiner.

L. M. PHYNES, Assistant Examiner.

3. A COPOLYMER OF TRIOXANE AND A CYCLIC FORMAL OF AN UNSATURATEDDIHYDRIC ALCOHOL HAVING 4 TO 10 CARBON ATOMS, SAID COPOLYMER HAVINGOLEFINIC DOUBLE BONDS IN THE MAIN CHAIN AND CONSISTING OF 80 TO 99.9MOLE PERCENT OF -O.CH2- UNITS AND 0.1 TO 20 MOLE PERCENT OF UNITS OTHERTHAN -O.CH2- DERIVED FROM THE CYCLIC FORMAL.